1. Field of the Invention
The present invention relates to a pivotal structure for a motor rotor of, e.g., a miniature heat-dissipating fan that includes a metal axle tube having a bearing mounted therein. An outer periphery of the metal axle tube is engaged with a stator bobbin. The metal axle tube is mounted in place very reliably, thereby allowing stable rotation of the rotor.
2. Description of the Related Art
U.S. Pat. No. 5,492,458 to Alex Horng issued on Feb. 20, 1996 discloses an electric fan includes a housing having a stub 11 formed in the center. A metal axle tube 4 has one end force-mounted in the stub 11 and an annular flange 43 formed in the other end. Two pole plates 30 and 32 are force-fitted on the axle tube 4, and a stator 3 is disposed between the pole plates 30 and 32. The metal axle tube 4 has a diameter greater than inner diameter of central holes 34 and 35 of the pole plates 30 and 32 and inner diameter of a central hole 21 in a circuit board 2. The diameter of the metal axle tube 4 is slightly smaller than that of a central hole 33 of the stator 3. Nevertheless, it is found that the stub 11 breaks if force mounting between the metal axle tube 4 and the stub 11 is too tight. On the contrary, the metal axle tube 4 will loosen in an undesired manner if the force mounting between the metal axle tube 4 and the stub 11 is too loose.